Proposition 2.4 [1]}
Let \(f:\prod _{i=1}^n{\mathcal {D}}_{k_i}\rightarrow {\mathcal {D}}_{k_0}\)  be a mix-valued logical function. Then there exists a unique matrix \(M_f\in M_{k_0\times k}\) , such that
\(f(x_1,\cdots ,x_n)=M_f\ltimes _{i=1}^n x_i.\) 
